Conventionally, as described in particular in “The Theory of Horology” by C. A. Reymondin et al., ISBN 978-2-940025-10-7, published by the Swiss Federation of Technical Colleges, Lausanne, the balances and balance springs are manufactured, and then sorted into a large number of grades. To form a sprung balance assembly capable of oscillating close to a certain oscillation frequency, a balance and a balance spring should thus each be taken from a grade capable of achieving close to this frequency, then the pair thereby formed should be adjusted to obtain the actual desired frequency, by adjusting the length of the balance spring, and/or by modifying the moment of inertia of the balance.
Consequently, a huge volume of goods in production is required to satisfy demand. Despite the goods in production, it is still necessary to carry out operations on the balance spring and balance, which are not ready for use.
The precision of frequency adjustment naturally depends on the range of each grade of balance spring and balance, which explains the high number of grades.